Interpretation of the transient variations in the time series of precipitation amounts in Seoul, Korea. Part I: Diurnal variation

Characteristics of temporal variations of precipitation for Seoul, Korea, h ave been examined using a 220-yr record. Precipitation records from modern rain gauges were used for 1908-96 together with the traditional Korean rain gauge precipitations for 1777-1907. The precipitation time series was part itioned into three precipitation regimes: wet period 1 (WP1; 1783-1883), th e dry period (DP; 1884-1910), and wet period 2 (WP2; 1911-96). The basic fe atures of the records were examined, and the diurnal variations derived fro m hourly precipitation were investigated. There were similarities between t he statistical characteristics of the time series for WP1 and WP2, but the DP showed many statistical characteristics different from WP1 and WP2. Diurnal cycles derived from the hourly precipitation rates in Seoul are gen erally consistent with previous observations in maritime areas, but some di fferences are apparent between the two WPs and the DP in the mean diurnal c ycle and its seasonal variation. The WPs show similar characteristics of di urnal cycle with a peak near 0600 LST and a broad evening minimum around 19 00-2400 LST during most of the years. The amplitude of the normalized diurn al cycle increases as precipitation intensity increases, and the timing for the morning peak is slightly earlier for the intense precipitation than fo r the light and moderate precipitation. In contrast, the morning maximum do es not manifest itself clearly during the dry period. The diurnal cycle is seen in all seasons. The morning peak during Changma (the rainy season over Korea) results mainly from intense precipitation events, which are confine d to a shorter period of the day than light or moderate precipitation.